There are conventionally known techniques for reducing noise of outdoor cooling unit for vehicular air conditioning apparatus. For example, “a vehicular heat exchange module which includes a fan unit disposed at the downstream side of a heat exchanger which is formed in a rectangular shape, the fan unit including a shroud having a bell-mouth and an annular opening, a propeller fan disposed in the annular opening, and a fan motor that rotates the propeller fan, wherein the fan unit is a unit having a single-fan configuration in which fan motor input power is not greater than a predetermined level, and the propeller fan is provided with two sets of winglets that are mounted to extend in a radius direction with a specific gap therebetween in a circumferential direction on both a pressure surface and a negative pressure surface at a proximal end of a blade” has been proposed (for example, see Patent Literature 1).
The vehicular heat exchange module described in Patent Literature 1 having the above configuration can prevent deviation of air flow and disturbance of flow caused by the deviated air flow being turned in the radius direction by the centrifugal force, thereby preventing deterioration of aerodynamic performance and increase of noise.
Further, there are techniques known for reducing noise of propeller fan. For example, “an axial flow fan having a plurality of blades disposed on the outer periphery of a cylindrical boss, wherein the blade has a cross section taken along a plane which extends in a radius direction from a rotation center through a proximal end of the blade that is in contact with the boss has a shape which curves in any position toward the outer periphery with the outer periphery being oriented to an air flow direction and having a horizontal angle which gradually increases toward the outer periphery, and the blade is a forward-swept wing with a forward swept angle formed by a straight line extending between the rotation center and the middle point of the proximal end of the blade and a straight line extending between the rotation center and the middle point of the outer peripheral edge of the blade being in the range of 20 to 40 degrees” has been proposed (for example, see Patent Literature 2).
The propeller fan described in Patent Literature 2 having the above configuration can further reduce air flow noise.